The work under this Center will include continuation of several clinical studies involving applications of transplantation immunology in patients as well as certain related laboratory experiments. The clinical studies will include 1) the randomized evaluation in kidney transplant recipients of a uniform preparation of horse anti-human thymocyte globulin in high dosage; 2) the continuing evaluation of frozen red cells for transfusion to avoid pre-immunization of recipients with HL-A antigens; 3) the development of more sensitive serological tests for pre-immunization; 4) the study of Azathioprine metabolism using C14 labelled material in selected patients; 5) the treatment of massive, lethal burns with transplanted skin from living, histocompatible donors with anti-thymocyte globulin immunosuppression; 6) the treatment of certain hereditary enzyme deficiencies (e.g. SanFilippo's syndrome, an alpha-glucosidase deficiency) by leukocyte or bone marrow infusion; 7) further exploration of the use of bone marrow transplants to treat severe aplastic Anemia. Related laboratory studies will include: 1) continuing studies of the mechanism by which passively infused humoral antibody can destroy rat skin grafts on appropriately immunosuppressed mice; 2) an analysis of the contribution of allogeneic differences determined at the various loci known to exist within the H-2 complex to mixed leukocyte reactions in vitro; 3) immunogenetic studies of special antigens on thymus derived and bone marrow derived lymphocytes in mice, and 4) studies of the genetic control of the class of antibody produced in mice in response to standard antigenic stimulation.